You’re in luck because Switzerland is dropping ALL Covid restrictions ( proof of vaccination, testing requirements, etc. ) on May 2.
And the train from Zurich’s airport directly to the Altstadt ( downtown) takes less than 15 minutes.
If Portugal still requires a negative Covid test for you to enter, you can provide them with one done the day before you fly into Europe. The US Embassy states that Portugal requires of all passengers at least 12 years old either an EU DIGITAL VACCINATION CERTIFICATE, or a negative Antigen Test taken no more than the day prior to arrival or a negative PCR test taken no more than 72 hours before arrival. The U.S. Embassy states that as of April 22, 2022 Portugal has not clarified whether the U.S. CDC Vaccination Card is acceptable, and so, until they do clarify this, the US Embassy advises that Americans 12 and older get a negative Covid Test before flying to Portugal.